In a tire manufacturing process, a test for inspecting a shape (profile) defect of a tire is performed in a final station. For example, in this test, a tire as an inspection target is subjected to a measurement using a laser displacement meter, while being rotated 360 degrees, to obtain tire shape data along a single line. Then, bulge and dent defects and a low-frequency undulation (run-out) of the tire are derived from the shape data to determine whether or not the tire is acceptable.
Recent years, in response to major tire manufacturers' appeals pointing out insufficiency of the shape measurement along only a single line, there has been increasingly employed a technique of emitting a sheet-shaped laser beam to a tire to measure shape data in the entire region of a measurement surface of the tire, and performing a determination as to the acceptability.
For example, the following Patent Literature 1 discloses a shape detection apparatus configured to maintain a positional relationship between a line-shaped beam emitting device and an imaging device in such a manner as to allow an angle between a tire surface and a line-shaped beam emitted from the line-shaped beam emitting means to be equal to an angle between the tire surface and a line extending from a reaching point of the line-shaped beam with respect to the tire surface to a center of an imaging element.
The following Patent Literature 2 discloses an apparatus which is operable to pick up a sample original image of a sidewall surface of a sample tire formed with a raised and/or depressed mark, to preliminarily extract a region of the raised and/or depressed mark from the sample original image and generate a height offset image, whereafter the apparatus is operable to subtract the height offset image, from an inspection image of a sidewall surface of an inspection target tire to inspect a shape defect of the inspection target tire, based on the resulting image.
The following Patent Literature 3 discloses a technique of checking inspection accuracy of an apparatus for inspecting a shape of a stator coil by using a light-section method, wherein a master workpiece which simulates a shape of a coil end of the stator coil is preliminarily provided as an inspection jig, and accuracy checking of the apparatus is performed using the master workpiece.
Meanwhile, deterioration in measurement accuracy of a shape inspection device is likely to lead to an undesirable situation where a tire having a shape defect is shipped. Thus, it is necessary to check inspection accuracy of the shape inspection device on a regular basis. In addition, it is desirable to allow the accuracy checking to be easily performed on a user side. In this regard, it is desirable that the accuracy checking can be performed without modifying software, e.g., without equipping a special measurement mode for the accuracy checking.
However, none of the Patent Literatures 1 and 2 includes any description about checking of inspection accuracy of the shape inspection device. In the Patent Literature 3, no consideration is taken for eliminating a need for modification of software, although consideration is taken for eliminating a need for modification of hardware.